Calculation of radiated emission from chassis connected to PCB with screw

Calculation technique to obtain radiated electric far-field from assembled device: chassis with PCB has been investigated. Circuit model including ground and power planes are created in PSPICE in order to calculate frequency spectrum of the current flowing through the screw at different location. Next, simplified 3D chassis model are created with simplified PCB model which does not have any traces or patterns. The relation between radiated electric field from the simplified model and the screw current is calculated from that 3D model. Lastly, the radiated electric field from the chassis with PCB has been calculated using both PSPICE circuit simulation results and the chassis 3D simulation results. The difference of far-field at different screw location from the calculation was up to 6 dB, which shows good correlation with measurement results.